In the Hitchhiker's Guide to the Galaxy, the titular book is a travel guide with all of the information in the universe. If that idea sounds overwhelming to you, you are not alone, which is why the book's cover has only two words on it: "Don't Panic."
That guidance can be helpful for bridge players as well. There's a lot of information and sometimes you find yourself in an obscure contract that seems impossible. Take a step back and say to yourself, "Don't Panic."'
Moysian fits (named for Alphonse "Sonny" Moyse) are simply 4-3 trump fits. These hands can be very tricky to play, but there's no reason to panic. As long as you keep your head, you should be able to handle these fits.
How do we wind up in Moysian fits? I usually blame partner. That said, you can wind up in a 4-3 fit in a number of ways—partner raised your four-card suit with three-card support and a singleton. Maybe partner made a takeout double. Possibly this was the result of Garbage Stayman or maybe partner didn’t realize that our overcall was only a 4-card suit and raised us with only 3 (good partners always have 4).
In an ideal world all of these machinations work out for a very specific reason--the hand with three trump would also have a side shortness that is protected by being in a trump suit. Of course sometimes partner’s side shortness is opposite our length or our honors and notrump would’ve been better. Oh well.
A couple of suggestions:
1) Be careful about getting rid of all the trump in the short hand. You don't want to be forced to ruff in the hand with 4 trump, so try to keep some trump in both hands until all your work is done.
2) Think about how many rounds of trump you should draw, but don’t be afraid of pulling trump. Sometimes your best bet is to treat the hand as a notrump hand and eliminate trump, but you should be sure that you have coverage everywhere.
Let's try a couple of hands to see how well you handle Moysian fits.
Ok, you overbid a little and partner’s hand isn’t exactly what the doctor ordered. LHO leads the K and then Q, RHO overtakes with the A and switches to the Q. What next?
You have two club losers and one diamond loser in addition to the two hearts you've already lost. What can you do? You need diamonds to be 3-2 so you can pitch two of your clubs on diamonds. Once you've figured that out, you now need to decide whether you can afford to draw trump.
If trump are 3-3, you can draw all the trump and still have a control, but you won't find that out until the third round of the suit. If you draw three rounds and trump are 4-2, you'll be in a lot of trouble. You can avoid drawing the last trump, but now your opponents will force you to ruff a heart when you lose your diamond. You will eventually lose a trump trick (and maybe more if the hand with 6 hearts also has four spades (unlikely, but these things happen).
So you definitely shouldn't draw all of the trump since you will have to lose another trick. You can afford 2 rounds, however as long as you keep an entry to hand. Win the Q in dummy, play two rounds of trump and then play a diamond, ducking. Now, the opponents can't do anything to hurt you.
The full deal is below. Wow East was stealing with her 4 bid, but there's not much you can do about it as you can only beat them 3.
Ok--one more deal.
You get to four spades. West leads the A and you see a respectable dummy, but wish your side had some more spades.
Partner was stuck after your double, and chose the cheapest option, understandably. LHO starts with the A, K, and then Q of hearts, RHO discarding the K. What do you do?
If you sit there complaining that 5 is cold, then you won't make the right choice. Here, you know you have two heart losers and two potential club losers. One of those losers will go away on the good diamond, but you have can't do anything about the second club. Since you have to lose it anyway, you should not ruff this trick. Instead, throw away a club. Now, if they continue to attack hearts, you can ruff high, draw four rounds of trump and claim as long as trump are 4-2. If you had ruffed, you would need trump 3-3 to make.
The full deal: